Magnetic control apparatus



Oct. 14, 1958 c. J. ADAMS ETAL MAGNETIC CONTROL APPARATUS Filed Jan. 28, 1957 tklllilifri INVENTORS s J. ADAMs,

CHARLE Ru SSELL A. BRowu BY 71(22: MM

ATTORNEY nited States Patent MAGNETIC CONTROL APPARATUS Charles J. Adams and Russell A. Brown, Bloomington,

111., assignors to General Electric Company, a corporation of New York Application January 28, 1957, Serial No. 636,572 6 Claims. (Cl. 307-106) Our invention relates to magnetic control apparatus and more particularly to magnetic amplifier type control elements, units and systems adapted to perform the elemental or logical control functions required in the automatic and semiautomatic operation of industrial tools and machinery.

In an application Serial No. 630,936, filed December 27, 1956, by Russell A. Brown there are disclosed pulse power responsive magnetic amplifier type circuits and devices suitable for use in static or contactless switching of electric currents or impulses in accord with basic logical or elemental control function which make up the control system. The circuits involved are described in this Brown application in connection with control devices known as or units and not units. The or unit provides an output signal when any one or more input signals is present, while the not unit provides an output at all times except when one or more input signals is present.

The instant invention is an improvement upon the invention of this application Serial No. 630,936 and has for its object the provision of a pulse power responsive magnetic amplifier type circuit and device capable of being switched between two stable electrical output conditions corresponding to off and on conditions, and of remaining in the prevailing condition whenever the power or control impulse is removed. Such devices have become known as on-off or memory units.

The term pulse power is used herein to mean a source of periodic pulses of electric voltage and current, each pulse having an abrupt rise and fall and having a much shorter duration than the duration of a half wave of sinusoidal current at 60 cycles. Preferably, the ratio of pulse time to no-pulse time during each .cycle is less than .1 and the voltage rise along the wave front occurs during less than 3 degrees of a sinusoidal wave at 60 cycles. For example, pulses having a width of 400 microseconds duration and occurring at a frequency of 120 pulses per second are suitable.

In general, in accord with the invention, a closed mag netic core of high permeability material such as Deltamax has wound thereon a gate winding, a feedback winding, a bias winding and at least one control winding. The gate and feedback windings are connected in series with each other and with a rectifier in a series load circuit arranged to receive power pulses. The bias winding is arranged to provide magnetic flux in the core opposing that produced by the gate and feedback windings. A capacitor is connected in the circuit to sustain current in the feedback winding during the intervals between power pulses. The value of this capacitor and the ratio of gate to feedback winding turns as well as the ratio of magnetic path length to total ampere turns is selected and constructed to be such that an unusually wide rectangular loop occurs in the input vs. output current characteristic curve. The circuit is biased along the central axis of this loop, and input signal current in either direction of a magnitude above predetermined threshold values cause the output current to switch with a snap action between stable on and off current level conditions. During this switching action the core is driven between positive and negative saturation conditions and remains in the prevailing saturated condition even after the signal or power is removed.

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof can best be understood by referring to the following description taken in connection with the accompanying drawing in which:

Figure 1 is a circuit diagram of a control circuit embodying the invention; and

Figure 2 is a typical input vs. output current characteristic of the memory unit incorporated in the circuit of Figure 1.

Referring to Figure 1, the invention is shown in one form in connection with a control circuit comprising a pulse and bias power supply 7, a magnetic amplifier type memory unit 8 and an electrical impedance 9 constituting the output load impedance of the magnetic amplifier unit 8. Memory unit 8 includes a magnetic core 10 of high permeability magnetic material, having wound thereon a gate winding 11, a feedback winding 12, a bias winding 13, and a pair of control windings 14, 15. Gate winding 11 and feedback winding 12 are arranged in flux aiding relation on core 10 and are connected in series with each other in a series circuit which includes a rectifier 16, a current limiting impedance, such as resistor 17, and output terminals 18, 19 for connection in series with electric impedance element 9 across a source 20 of power pulses in power supply 7. A capacitor 22 is connected in parallel with feedback winding 12, resistor 17 and the load impedance 9 connected across output terminals 18, 19. If the impedance of load impedance element 9 is great enough, resistor 17 may be omitted.

Bias winding 13 is connected through input terminals 24 to a source of unidirectional current 25 in power supply 7 and is arranged to produce magnetic flux in core 10 opposing the flux produced therein by gate winding 11. Control windings 14 and 15 are arranged to produce magnetic signal fluxes in opposite directions relative to one another in core 10; and thus, control winding 14 introduces magnetic flux opposing the gate winding flux while control winding 15 introduces magnetic fiux aiding the gate winding flux.

In accord with an important feature of the invention,

feedback winding 12 is constructed and arranged to exert a magnetomotive force in core 10 of about the same order of magnitude as that exerted by gate winding 11. Thus, feedback winding 12 may have from 0.5 to 1.2 times the number of turns of gate winding 11. Excellent results have been obtained with a feedback winding-togate winding turn ratio of 0.8. As will be explained hereinafter this unusually large feedback magnetomotive force results in an unusually wide rectangular loop, as illustrated in Figure 2, in the signal vs. output current characteristic curve of the circuit, which loop is of sufiicient width to enable the circuit to function as a memory unit. This is in contrast with prior circuits Where the feedback winding is only for the purpose of providing a snap acting characteristic and is constructed and arranged to exert only a small percentage, typically about one fifth (0.2) of the magnetomotive force provided by the gate winding.

In the over-all operation of the control circuit of Figure 1 a bias current, of a magnitude determined in a manner to be explained, is supplied to bias winding 13 from terminals 25 of power supply 7 and power pulses are supplied to the load circuit of magnetic amplifier unit 8 from terminals 20 of power supply 7. The voltage of each power pulse is applied across gate Winding 11 through rectifier 16 and through capacitor 22 in parallel with feedback winding 12, resistor 17, and load impedance 9. With proper signal currents (as explained hereinafter), this power pulse produces a magnetomotive force in core which quickly drives the core to saturation whereupon gate Winding 11 conducts or fires, passing a pulse of current to charge capacitor 22. After the passage of the power pulse, capacitor 22 discharges through feedback winding 12 and resistor 17 thereby sustaining, during the usual relaxation period, flux in core 10 proportional to the magnitude of load current flowing during the power pulse. The output current in load impedance 9 has a sawtooth wave shape as shown at 30. The magnetic flux due to feedback winding 12 is in the same direction within core 10 as that produced by gate winding 11 during its conducting period. it will be observed that capacitor 22 cannot discharge through gate winding 11 because of the presence of rectifier 16. The rate of discharge of capacitor 22 is determined by the impedance of feedback winding 12, resistor 17 and load 9.

Referring to Figure 2, presuming no bias current in winding 13 and core 10 in a positively saturated condition, a unidirectional signal current supplied to control winding 14 in a direction to produce magnetic flux in core 10 opposing that produced by gate and feedback windings 11 and 12 produces no effect upon the impedance of gate winding 11, which continues to pass the entire power pulse, until the magnitude of input signal current (indicated by the letter D) generates signal flux sufiicient to begin to overcome the saturating effects produced by the presence of rectifier 16, feedback winding 12, and capacitor 22. Once the magnitude of signal current begins to overcome the saturating effects of these components and thereby begins to hold off and decrease the duration of the power pulses passing to the load impedance 20, the amplitude of feedback current passing through Winding 12 during the relaxation period is also reduced. As a consequence, core 10 is not driven so deeply into the saturation region and the cumulative degenerative effect of these changes is to cause the core quickly to snap from a complete positively saturated condition into a complete negatively saturated condition in which the only load current flowing is the magnetizing current of the core. A similar cumulative regenerative efiect occurs when the signal current amplitude decreases to a point indicated by the letter R where the load current begins to increase whereupon the core quickly snaps from complete negative saturation to complete positive saturation. Because of the large magnetomotive force introduced by the great number of feedback winding turns, the signal current D at which the core snaps from complete positive saturation to complete negative saturation is quite different from the signal current R required to snap the core from complete negative saturation to complete positive saturation. The wide rectangular input current vs. output current characteristic curve or loop L results. It will be appreciated that this loop L also represents the signal flux vs. output current characteristic of the circuit.

In the operation of the circuit of Figure 1 as a memory unit, unidirectional current is supplied to bias winding 13 of a magnitude B sufficient to bias core 10 along an axis X in the center of this rectangular loop L. The value of this biasing current B thus falls midway between the value R at which output current snaps on and the value D at which the output current snaps off.

When the core 10 is biased in this manner, a signal current Sp through control winding 15 in a direction which may be termed positive aiding the gate winding flux and having a magnitude sufficient to drive the core beyond the forward knee (point r) of loop L will cause the unit to snap quickly to complete positive saturation and pass a high current to the load impedance element 9. If the core is already in its positively saturated condition '4 when the control signal is supplied to control winding 15 this will have little or no effect upon the unit.

If a control signal current Sn is supplied to control winding 14 producing flux therein in a direction which may be termed negative opposing the gate winding flux and having a magnitude sufiicient to drive the core beyond the rearward knee (point d) of loop L, the core will be quickly driven from complete positive saturation into complete negative saturation thereby reducing the load current to its minimum value. If the core is already in negative saturation when this negative control signal occurs there will be little or no effect upon the unit.

An important feature of the invention is that in the absence of control signals on either control winding 14 or control winding 15 the core remains in its prevailing saturated condition either positive at point P along the bias axis X or negative at point N along this axis X. Moreover there is a considerable region W of loop L where minor differences in biasing current or in small signal currents will not noticeably affect the saturation or output current level condition of the unit. This stability of the circuit is also improved if the magnetic path length in core 10 is made fairly long relative to the total ampere turns thereon. The ratio of magnetic path length to ampere turns should be considerably above 1.0, and preferably about 2.75. The unit thus has two distinct stable conditions of output current level and can be switched between these two current level conditions by the application of control signals to either control winding 14 for turning the unit off or to control winding 15 for turning the unit on. Alternatively, a single control winding such as winding 14 may be used and the signal current supplied thereto in opposite directions in order to accomplish this switching in both directions.

Another important feature of the invention is that despite the great number of feedback turns, the integrated magnitude of currents induced in the feedback winding 12 by transformer action from the gate winding 11 is only a small percentage of the currents resulting therein from the discharge of capacitor 22. This is due to the short duration of gate winding pulse power current relative to the duration of feedback winding current. Therefore, the effect of the feedback current is not masked and can function to give the wide rectangular input vs. output current loop with snap acting characteristic as previously disclosed. Similarly, the integrated magnitude of current induced in the control windings 14, 15 by transformer action from the gate winding 11 is only a small percentage of the normal control current magnitude so that the control signal is not masked and there is no appreciable effect upon the speed of response of the circuit.

In the construction of a typical memory unit 8, core 10 is a rectangular loop of stacked laminations of Deltamax or similar high permeability magnetic material having a magnetic path length of 5.5 inches and a cross sectional area of .059 square inch. All of the gate, feedback and control windings are of number 34 copper wire having a diameter of 0.0063 inch while the bias winding 13 is of number 28 copper wire having a diameter of 0.0126 inch. Bias winding 13 has 8 turns, control windings 14 and 15 each have 500 turns, gate winding 11 has 1,000 turns and feedback winding 12 has 700 turns. Rectifier 16 is a small germanium or silicon diode and capacitor 22 has a capacitance of 2 microfarads while resistor 17 has a resistance of 7,500 ohms. The power pulses supplied from power supply 20 typically have an amplitude of 55 volts, a duration of 500 microseconds and a pulse repetition frequency of pulses per second. A typical bias current is 0.390 ampere.

Although we have shown a particular embodiment of the invention, many modifications may be made and we intend by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A pulse power responsive magnetic amplifier c0n trol circuit comprising a rectifier, a magnetic core of high permeability, a gate winding and a feedback winding on said core connected in flux aiding relation and in series circuit with each other and with said rectifier for connection in series with an electric impedance across a source of pulse power, means connected to said feedback winding for sustaining current through said feedback winding during the intervals between power pulses, said feedback winding being constructed to produce a magnetomotive force in said core of the same order of magnitude as said gate winding to provide a relatively wide rectangular loop in the signal flux vs. output current characteristic of the circuit, means for biasing said core within the region of said loop, and means for introducing signal fluxes of opposite polarity in said core.

2. A pulse power responsive magnetic amplifier control circuit comprising a rectifier, a magnetic core of high permeability, a gate winding and a feedback winding on said core connected in flux aiding relation and in series circuit with each other and with said rectifier for connection in series with an electric impedance across a source of pulse power, a capacitor connected to said feedback winding for sustaining current through said feedback winding during the intervals between power pulses, said feedback winding having from .5 to 1.2 times the number of turns of said gate winding to provide a relatively wide rectangular loop in the input vs. output current characteristic of the circuit, means including a biasing winding on said core for biasing said core at a level substantially along the central axis of said loop, and means including at least one control winding for receiving input currents to introduce signal fluxes of opposite polarity in said core.

3. A pulse power responsive magnetic amplifier control circuit comprising a rectifier, a resistor, a magnetic core of high permeability, a gate winding and a feedback winding on said core connected in flux aiding relation and in series circuit with each other and with said rectifier and resistor for connection in series with an electric impedance across a source of pulse power, a capacitor connected in parallel circuit relation with said feedback winding for sustaining current through said feedback Winding after the passage of a power pulse supplied to said series circuit, said feedback winding having in the neighborhood of 0.8 times the number of turns of said gate winding to provide a snap acting switching action in said core whereby said circuit switches from a low output current level to a high output current level at one magnitude of signal flux and switches from high output current level to a low output current level at a different magnitude of signal flux, means including a bias winding on said core for biasing said core to a level intermediate said switching signal flux magnitudes, and means including control windings on said core for introducing signal fluxes of opposite polarity in said core.

4. A pulse power responsive magnetic amplifier control unit comprising a rectifier, a magnetic core of high permeability, a gate winding, a feedback winding, a bias winding, and at least one control winding on said core, said gate winding and feedback winding being arranged in flux aiding relation and in series circuit with each other and with said rectifier for connection in series with an electric impedance across a source of pulse power, and a capacitor connected in parallel circuit relation with said feedback winding, said feedback winding having from 0.5 to 1.2 times the number of turns of said gate winding.

5. The pulse power responsive control unit of claim 4 wherein the ratio of mangetic path length in the core to total ampere turns is considerably above 1.0.

6. The pulse power responsive magnetic amplifier control unit of claim 5 comprising a resistor connected in series circuit relation with said series circuit and in parallel circuit relation with said capacitor.

No references cited. 

